Tunable semiconductor lasers are often used for applications in which an occasional but precise tuning of wavelength is required. They can provide excellent wavelength stability and are typically manufactured as monolithic photonic integrated circuits (PICs) in a gain medium such as a III-V semiconductor material. However, they are expensive to manufacture as a result of the need for multiple epitaxial re-growth steps. To date, demonstrations have been relatively slow to tune, making them inadequate for certain applications.
Particularly in applications where the precise wavelength of the laser is not so important, there is a need for tunable lasers with a wide tuning range (>30 nm) but with fast switching speeds (of less than 100 ns or even more preferably less than 10 ns). Furthermore, in applications involving high data speeds and high device packing density, power efficiency is critical for technology adoption.
Silicon-on-insulator (SOI) lasers have become increasingly popular since SOI provides a practical, power efficient and cost-effective platform for the construction and integration of optical devices. Of course, the major challenge for SOI photonic integrated platforms is the fact that silicon is not an optical gain medium and does not therefore form an ideal medium for photonic circuits incorporating lasers. A common technique is to introduce a piece of gain material such as III-V gain material (often referred to as a gain chip) to a SOI photonic integrated circuit. An example of such a laser can be found in U.S. Pat. No. 6,101,210. A tunable laser constructed on a SOI PIC is disclosed in U.S. Pat. No. 8,559,470.
One drawback of such a design is the high optical power loss, particularly due to coupling between the waveguides formed from the silicon substrate and any waveguides in optical devices placed in, grown onto, or otherwise incorporated into the platform. Thus, there is also therefore a particular need for an SOI laser with an improved power efficiency.